Disk drives are widely used in computers, consumer electronics and data processing systems for storing information in digital form. The disk drive typically includes one or more storage disks and one or more head gimbal assemblies. Each head gimbal assembly includes a slider having an air bearing surface, and a data transducer that transfers information to and from the storage disk. The rotation of the storage disk causes the slider to ride on an air bearing so that the data transducer is at a distance from the storage disk that is referred to as a “head-to-disk spacing”.
Because today's disk drives utilize storage disks having increasingly high densities of data tracks, decreasing the head-to-disk spacing has become of great importance. However, this desire for a very small head-to-disk spacing must be balanced with tribological concerns in order to avoid damage to the data transducer and/or the storage disk, as well as loss of data. Thus, the range between head-to-disk contact and a desirable head-to-disk spacing has become extremely small, requiring an increasingly more accurate control system.
During in-situ usage of the disk drive, the temperature of the slider typically varies. For example, during a write operation, the electrical resistance of the write element generates heat in and around the data transducer, resulting in thermal expansion of the write pole tips toward the storage disk. The situation is commonly referred to a write pole tip protrusion (“WPTP”). If the WPTP is too extensive, the slider can unintentionally contact the storage disk (head-to-disk contact), causing off-track writing, damage to the slider or damage to the storage disk. Conversely, during read operations, the temperature of the slider can be somewhat lower, resulting in less thermal expansion and a greater head-to-disk spacing. Under this circumstance, reading errors can occur due to the increased head-to-disk spacing.